7208

• UCREFRP Catalog Number: 7208
• Author: Lyons, J.
• Title: Green River Channel Characteristics Below Flaming Gorge.
• USFW Year: 1989.
• USFW - Doc Type: Denver, Co.
• Copyright Material: NO

7
A step-backwater computer program (USBR, [7]) was used to compute the water
surface elevation profile for the Dinosaur Quarry and Ouray Refuge, and
Willow Creek sites for o f di5_c a including the computed effective
flow.
The effective flows computed for these sites did not approximate bankfull flow
(the discharge where flow just begins to leave the main channel and occupy the
flood plain) as defined by the cross section information collected in 1986
t e bankfull flow redicted the com ter simulat' ns a eede
c ive 1 bu was less t an the ma imum flow given in the
the cal ted of efow
ranges above for each si e.
In the hydraulic computations performed using the step-backwater program, a
roughness n value was selected for use in computing water surface profiles
through a reach of channel. At the Quarry site, seven transects spaced over
4,260 feet were measured at a discharge of 5,400 ft3/s. At the Refuge site,
seven transects were measured in 4,840 feet of channel at a discharge of
9,940 ft3/s. At the site below Willow Creek, three transects spaced over
2,740 feet of channel were measured at a discharge of 5,230 ft3/s.
Calibrated roughness n values for the channel and overbank portions of each
transect were derived by adjusting these roughness values to obtain a computed
water surface profile that closely matched the measured water surface profile
through each reach. These calibrated values were used to compute the water sur-
face profiles in the study reach for the range of flows of interest.
Application of these calibrated roughness values to larger discharges assumes
that no roughness changes occur over the range of flows of interest. Also, the
channel measurements used in this analysis describe the Green River channel
following the high flow years of 1983, 1984, and 1986. These conditions may not
represent average channel conditions for the entire postreservoir period used
in calculating the effective flow.
Mean Annual Sand Load
The sand-load discharge rating curves (figures 10, 12-15) were used with flow
duration data from the gauges near Jensen, Utah, and at Green River, Utah, for
1965-1987. For the Quarry site and Refuge site, the mean annual sand-load
discharge for this period is 1,480,000 tons/year (table 1). These estimates
are based upon the Jensen gauge mean daily flow data and the suspended sand
load rating curve developed from the entire gauge history.
For the site downstream of Willow Creek, the mean annual sand load is
2,910,000 tons/year (table 2). The adjusted (see above for adjustment details)
mean daily flows from the Green River, Utah, gauge were used in this estimate.
The suspended sand-load rating curve for the Ouray gauge was used in
conjunction with the adjusted discharges.
At Green River, Utah, the mean annual sand load is 3,090,000 tons/year
(table 3). This estimate is based upon the mean daily flow record from the
Green River, Utah, gauge and the suspended sand-load rating curve developed
for this gauge using the entire gauged history; For the Duchesne River,
sediment rating curve developed for the Geological Survey gauge near Randlett
(figure 14) was used along with the mean daily flow record from this gauge